The door that served a key role in the final scenes of Titanic — and in the years since has become the subject of much internet debate — has sold at auction for a whopping $718,750. That astronomical figure shows just how important that door has become in the fandom around James Cameron’s massively popular ’90s drama — still the fourth biggest movie in history. If it’s not the most famous door in history, it’s got to be a close second. (The only thing that even seems to be in the conversation is the door Jack Nicholson demolishes with an ax before screaming “Here’s Johnny!” through it in The S…